Reactive Intermediates in the Photolysis of Furan, Thiophene and Pyrrole: The Dewar and the Ring Contraction forms

Abstract

Five-member aromatic heterocycles have been known to undergo scrambling of the ring atoms upon photolysis. These reactions are characterized by their selectivity and several mechanisms have been proposed involving the intermediacy of a variety of isomeric structures, in particular, the Dewar and the ring-contracted forms. We have carried out a series of low-temperature argon-matrix photolysis and solution phase trapping experiments on the parent furan, thiophene and pyrrole in order to obtain evidence on the formation of these reaction intermediates.